Abstract:

Exponential nutrient delivery can bring about a steady state of nutrition in the plant and improve nutrient uptake,and hence accelerate seedling growth.An exponential fertilization trial was conducted with seven N dose levels (applying a total of 0,50,100,200,300,400,600 mg·seedling^-1in this experiment) of nitrogen to assess the effects of different nitrogen levels on growth and foliar nutrient status of Betula alnoides seedlings.The objective of this study was to reveal the nitrogen demand and determine the optimal nitrogen amount for B.alnoides seedlings.It was indicated that:1) Ground diameter,height,biomass and leaf area of B.alnoides seedlings increased with the increase of nitrogen supply,up to 200 mg·seedling^-1,after then growth performance and biomass were unchanged and leaf area remarkable decreased.2) The leaf nitrogen,phosphorus,and potassium concentrations increased in general as the nitrogen addition increased when nitrogen supply was more than 200 mg·seedling^-1,the leaf nitrogen and potassium concentrations continued to increase because of luxury consumption characterized by increased the internal nutrient concentrations without significant changes in total dry mass,while the leaf phosphorus concentration tended to be stable with nitrogen supply above 100 mg·seedling^-1,suggesting that phosphorus was sufficient for plant growth.3) Critical level approach was used for identifying N,P and K deficiencies by means of foliar analysis in B.alnoides seedlings,and the critical values of N,P,and K were 37.8,4.1,and 24.4 g·kg^-1,while their optimal concentrations ranged from 37.8 to 59.1,4.1 to 6.3 and 24.4 to 34.7 g·kg^-1,respectively.Based on these data,it could be inferred that 200-400 mg·seedling^-1would be the optimal nitrogen amount for B.alnoides seedlings.

Key words: Betula alnoides, exponential fertilization, growth performance, leaf nutrient concentration, nitrogen